Toxicon 50 (2007) 106–119 Inﬂuence of inorganic nutrition on growth and PSP toxin production of Alexandrium minutum (Dinophyceae) from Cork Harbour, Ireland Nicolas Touzet a,Ã , Jose M. Franco b , Robin Raine a a The Martin Ryan Institute, National University of Ireland, Galway, Ireland b U.A. Fitoplancton To´xico, CSIC-IEO, Apto. 1552, Vigo, Spain Received 28 July 2006; received in revised form 1 March 2007; accepted 2 March 2007 Available online 12 March 2007 Abstract The physiological response of the PSP toxin producing dinoﬂagellate Alexandrium minutum isolated from the Irish coast was assessed after modulating the initial concentrations of nitrate and phosphate in batch cultures. The cell growth in cultures of strain CK.A02 was primarily controlled by nitrate availability. In all experiments, only gonyautoxins 2 and 3 (GTX2 and 3) were synthesized along the different growth phases, with GTX3 dominating (E80%) at all stages, making the GTX2–3 toxin proﬁle a possible population marker of A. minutum in Cork Harbour. The cellular toxin quotas remained low and relatively stable at around 2 pg cell 1 , except when high N:P ratios were initially used for culture inoculations; in these conditions PSP toxins accumulated up to 14 pg cell 1 . Due to the composition of the toxin proﬁle, the toxicity of strain CK.A02 was generally relatively low (from 1.1 to 1.7 pg STX eq cell 1 ) in comparison with strains from other geographic areas except when phosphate limiting culture conditions were applied (maximum of 12.5 pg STX eq cell 1 ). Results showed that sufﬁcient soluble protein quotas were necessary to observe the intra-cellular accumulation of PSP toxins in phosphate limiting conditions, highlighting also the requirement of adequate nitrogen supplies. The possible existence of localized toxicity hot spots in the ﬁeld, linked to the accumulation of PSP toxins within A. minutum cells as a metabolic response to adverse environmental conditions, could potentially increase risks for shellﬁsh farming operations. r 2007 Elsevier Ltd. All rights reserved. Keywords: Alexandrium minutum; Harmful algal blooms; Paralytic shellﬁsh poisoning 1. Introduction Over the past decades, harmful algal blooms (HABs) have become a signiﬁcant global concern as a food safety, environmental and socio-economic issue (Hallegraeff, 1993). Injurious algal species involved have had deleterious effects on water quality and aquaculture, and have sometimes led to severe human intoxications through the con- sumption of contaminated shellﬁsh (Adams et al., 1968; Hoagland et al., 2002). Some species among the marine dinoﬂagellate genus Alexandrium are recognized as being responsible for paralytic shell- ﬁsh poisoning (PSP). The highly potent neurotoxic ARTICLE IN PRESS www.elsevier.com/locate/toxicon 0041-0101/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.toxicon.2007.03.001 Ã Corresponding author. Tel.: +353 91 493231; fax: +353 91 525005. E-mail address: nicolas.touzet@nuigalway.ie (N. Touzet).